The present invention relates to an improved barrier to hydrogen-isotope permeation at elevated temperature. It has application in any hydrogen isotope containment system, but is particularly useful in systems containing tritium at high temperatures where heat is to be transferred between corrosive fluids. For instance, the barrier may have application in cooling systems for plasma confinement devices and thermonuclear reactors. Systems of these types are illustrated in U.S. Pat. No. 3,957,597, May 18, 1976, entitled "Process For Recovering Tritium From Molten Lithium Metal" , by Maroni; Proceedings Of The First Topical Meeting On The Technology Of Control Nuclear Fusion, "An Environmental Impact Study Of A Reference Theta-Pinch Reactor (RTPR)" , CONF-740402 Pl, April 16-18, 1974, San Diego, California; Study Of A Reference Theta-Pinch Reactor (RTPR)" , Vols. 1 and 2, ANL-8019/LA-5339, February 1974 and March 1975.
A potentially significant effect of a fusion power plant is leakage of tritium to the environment. Tritium is considered to be a "low-hazard" isotope because of the low beta energy associated with its decay and because the biological half-life of tritium injested in the human body as HTO, either by breathing or drinking, is short (approximately 10 days). However, foods grown in a tritium environment may allow tritium to replace hydrogen in some carbohydrates. Because of this less direct hazard considerable care must be taken to prevent tritium leakage from any system that contains this isotope. Tritium is also a valuable fuel in D-T thermonuclear reactions and a valuable tracer isotope, thus adding an economic incentive for its containment.
Metal composites have previously been suggested by the inventor for use as hydrogen isotope barriers in fusion reactor reference designs. For instance, in "An Analysis Of Tritium Distribution And Leakage Characteristics For Two Fusion Reactor Reference Designs" CEN/CTR/TM-9, Mar. 13, 1974, various two and three-layer composites have been proposed. In particular, copper, aluminum, tungsten, molybdenum or gold have been suggested as intermediate layers between outer layers of stainless steel and high-nickel alloys. These composites, either, produce only a few fold decrease in permeability over that of the outer layers used alone or are difficult to fabricate.
The inventor being aware of the shortcomings of the prior art has as an object of his invention to provide an improved barrier to hydrogen-isotope permeation.
It is a further object of the invention to provide a barrier that exhibits reduced hydrogen-isotope permeability without incurring significant increases in wall thickness or resistance to heat transfer.
It is also an object of the invention to provide a barrier to hydrogen isotopes that can reduce permeation by at least 30 or more fold below equal thicknesses of usual heat and corrosion resistant construction materials.
It is a further object of the invention to provide composite construction materials that can be used in complex heat transfer systems where different material-compatibility problems are associated with various coolants and working fluids.